INTRODUCTION
The invention relates to a process and apparatus for the fast cleaning of filter elements, especially filter cartridges, where solutions of organic matter, containing finely divided, highly dispersed suspended substances as impurities, are separated under pressure from the filter cake built up and are ready for further use in no time at all.
Solutions of this kind, e.g., are obtained while extracting fats and oils by means of organic solvents. Furthermore, such solutions are employed in many fields of organic chemistry, e.g. during the separation of mineral oil, the manufacture of paper and cellulose, the production of dyestuff, drugs, starting products of plastic material, juices, etc.
In addition to the so-called pressure leaf filters, disk filters, filter presses, etc., cartridge filters turn out to be especially successful, when the contaminating suspended substances and perhaps the auxiliary filtering material show satisfactory surface properties to allow the solution to pass over from the turbid liquid to the interior of the filter elements absorbing the pure solution as quickly as possible.
During the filtration of considerable quantities of liquids per unit of surface, cartridge filters are of special advantage as often as the solution shows a hydrophobic character and a low portion of turbid substances. The low-priced production of cartridge filters with a relatively large filtering area on a minimum space make them an indispensable aid in the engineering chemistry for that reason alone.
Cartridge filters are preferably used as pressure filters, i.e. the turbid liquid to be filtered is pressed against the (outer) surface of the filter elements, in the course of which procedure the impurities to be separated are retained on the filtering surface as a so-called filter cake, while the pure solution is drawn off from the inside of said cartridges.
Multiple cartridge filters can have a filtering area of up to 300 m.sup.2 (and more) which in pressure vessels are charged with 100 bar and more.
Cartridge filters often work according to the deposit filtration principle, i.e. the turbid liquid to be filtered either moves in a circular course through the filter units over and over again until a filter bed of turbid matter has built up on the surface of said filter cartridges which then functions as filter aid, or a so-called filter aid is added to the turbid liquid to be filtered which helps to build up the filter bed on the surface of said cartridges.
Cartridge filters are a true technical aid every time the filter cake built up of filtering material and turbid substances on the surface of the cartridges can be easily removed without having to open the filter unit or even disassemble it.
However, it is known that it is typical for many substances to be separated from a turbid liquid not to fall from the filtering surface or not be separated therefrom without extreme difficulties. In many cases, the filter cake separates from the filtering surface partially or in layers only; consequently, during the following filtration cycle, either part of the filtering surface is available only, or the filtration capacity is already exhausted after the building up of a new, thin layer of cake.
The purpose of the present invention is to overcome the before-mentioned difficulties in removing the filter cake from the surface of cartridge filters completely and, in that way, to increase the capacity of cartridge filters (per unit of time).